1. Field of the Invention
The present invention relates to a broadcast receiving device and a broadcast reception and output method, particularly to those that are made adaptable to the conditions of received broadcast waves that change with the move of a mobile body furnished with such equipment by taking advantage of both digital and analog broadcast merits.
2. Description of the Related Art
With digital television broadcasting about to begin in Japan, the development of digital TV receiving equipment for mobile applications is in progress. Japanese Patent Laid-Open Publication No. Hei 9-307517, for example, proposes equipment related to digital television broadcasting. Digital broadcasting has advantages in that digital broadcasting can provide higher quality images and sound over analog broadcasting.
As is well-known, digital TV broadcast receivers assure a higher quality of reception by carrying out error correction. If, however, the electric field of received broadcast waves is below a certain level, error correction cannot be performed and no images can be reproduced. This phenomenon is referred to as a cliff effect. When providing a digital broadcast receiver installed on a mobile body, the field intensity of received broadcast signals change as the body moves. Thus, there is a possibility that the field intensity of a received signal will become so low that no images can be obtained due to the cliff effect.
Analog signals have a demerit that ghosts or blurred colors may occur, due to the affect of multiple paths, even when the power of received broadcast waves is sufficiently large. However, unlike digital broadcasts, analog broadcasts are free from the cliff effect. Even when the field intensity of received broadcast waves becomes low during the move of a mobile body equipped with an analog broadcast receiver, the receiver can continue to generate video and audio outputs, though image and sound quality decrease.
As described above, digital broadcasts have higher quality, but no images can be obtained from them when the field intensity of received broadcast waves is below a certain level. In contrast, analog broadcasts can continue to produce images, no matter how low the field intensity of received broadcast waves becomes low.
An object of the present invention is to provide a broadcast receiver and a broadcast reception and output method that are adaptable to the conditions of received broadcast waves that change with the move of a mobile body furnished with such equipment through the selective use of digital and analog broadcast characteristics.
The broadcast receiver equipment according to the present invention comprises a digital broadcast receiver portion for receiving at least one digital broadcast channel; an analog broadcast receiver portion for receiving analog broadcasts including a channel for transmitting the same content broadcast as on at least one of the digital broadcast channels that can be received by the digital broadcast receiver portion; a receive condition sensing means for sensing the condition of either or both of the digital and analog broadcast waves received by the digital and analog broadcast receiver potions; a channel selection switch for carrying out channel selection, based on predetermined processing; selection means for selecting either the digital or analog broadcast when the channel selection switch has selected a pair of digital and analog channels from which same content broadcasts are received, according to the conditions of received broadcast waves, as sensed by the receive condition sensing means; and a broadcast output means for outputting the selected broadcast.
In the broadcast receiver of the present invention, when broadcasts of the same content are received from a pair of digital and analog channels which have been selected by the channel selection switch, based on predetermined processing, the selection means selects either the digital or analog broadcast, according to the conditions of either or both of the digital and analog broadcast waves received by the digital and analog broadcast receiver portions, as sensed by the receive condition sensing means, and the broadcast output means outputs the selected broadcast. Thus, the present invention enables selective output of digital or analog signals of better quality, because the broadcast output is switched between the received digital and analog broadcasts, according to the conditions of either or both of the digital and analog broadcast waves received by its digital and analog broadcast receiver portions. The broadcast in the above description can be exemplified by TV broadcasting, but are not limited to this, and any kind of broadcasting, such as radio broadcasting, may be applicable to the present invention. The xe2x80x9cpredetermined processingxe2x80x9d of the channel selection switch includes operation by the user and an automatic search executed when the receiver is powered up.
This broadcast receiver of the present invention may operate so that the receive condition sensing means senses the conditions of the digital broadcast waves received by the digital broadcast receiver portion. If this is implemented, the device can switch over between digital and analog broadcasts to be output, according to the conditions of received digital broadcast waves that produce clearer sound and images.
When the broadcast receiving equipment according to the present invention is intended to perform digital/analog broadcast switching according to the conditions of received digital broadcast waves, its receive condition sensing means may detect the error rate of packets during the demodulation of the received digital broadcast signals as an index of the conditions of the received waves. If this is implemented, the device can easily determine whether the strength of the received digital broadcast is sufficient to obtain output such as images. When operating in this manner, the broadcast receiving equipment of the present invention can be preset so that its selection means selects the digital broadcast if the error rate of packets detected as the index of the conditions of the received digital broadcast waves is less than a predetermined rate or select the corresponding analog broadcast if this error rate is equal to or greater than the predetermined rate.
Alternatively, when the broadcast receiving equipment according to the present invention is intended to perform digital/analog broadcast switching according to the conditions of received digital broadcast waves, its receive condition sensing means may detect the received power level of the received digital broadcast signals as the index of the conditions of the received digital broadcast waves. Because the received power level is closely related to the received wave conditions, more adequate digital/analog broadcast switching can be performed according to the received power level. When operating in this manner, the broadcast receiving equipment of the present invention can be preset so that its digital/analog selection means selects the digital broadcast if the received power level is equal to or higher than a predetermined level or select the corresponding analog broadcast if this level is lower than the predetermined level.
The broadcast receiver of the present invention also may operate so that its receive condition sensing means senses the conditions of the analog broadcast waves received by the analog broadcast receiver portion. If this is implemented, the equipment can switch over between digital and analog broadcasts to be output, according to the conditions of received analog broadcast waves.
In the broadcast receiver according to the present invention, furthermore, the receive condition sensing means may comprise a received video conditions sensing means for sensing the conditions of the video of the received broadcast waves and a received audio conditions sensing means for sensing the conditions of the audio of the received broadcast waves. Moreover, the selection means may comprise a video selection means for selecting either the video of the digital broadcast or the video of the analog broadcast, according to the received video conditions as sensed by the received video condition sensing means, and a audio selection means for selecting either the audio of the digital broadcast or the audio of the analog broadcast, according to the received audio conditions sensed by the received audio condition sensing means. This configuration, if implemented, enables the equipment to selectively output more adequate video as well as audio from either digital or analog broadcasts.
When the broadcast receiver according to the present invention is intended to perform broadcast switching separately for video and audio in the above configuration, its received video condition sensing means may detect the error rate of video packets during the demodulation of the received digital broadcast signals as the index of the received video condition and its received audio condition sensing means may detect the error rate of audio packets during the demodulation of the received digital broadcast signals as the index of the received audio condition. If this is implemented, the equipment can easily determine whether the video and audio obtained from the digital broadcast are adequate. When operating in this manner, the broadcast receiving equipment of the present invention can be preset so that its digital/analog video selection means selects the video of the digital broadcast when the error rate of the video packets detected by the received video conditions sensing means is less than a predetermined rate and select the video of the analog broadcast when this rate is greater than or equal to the predetermined rate and its audio selection means selects the audio of the digital broadcast when the error rate of the audio packets detected by the received audio conditions sensing means is less than a predetermined rate or selects the audio of the analog broadcast signals when this rate is greater than or equal to the predetermined rate.
Alternatively, when the broadcast receiver according to the present invention is intended to perform digital/analog broadcast switching separately for video and audio, its received video conditions sensing means may detect the received power level of the video of the received digital broadcast signals as the index of the received video condition and its received audio conditions sensing means may detect the received power level of the audio of the received digital broadcast signals as the index of the received audio condition. Because the received power level is closely related to the received wave conditions, higher quality video and audio outputs can be obtained from either digital or analog broadcasts according to the received power level. When operating in this manner, the broadcast receiving equipment of the present invention can be preset so that its video selection means selects the video of the digital broadcast if the received power level of the video detected by the received video condition sensing means is greater than or equal to a predetermined level or selects the video of the analog broadcast if this level is below the predetermined level and its audio selection means will select the audio of the digital broadcast if the received power level of the audio detected by the received audio conditions sensing means is greater than or equal to a predetermined level or select the audio of the analog broadcast if this level is below the predetermined level.
Furthermore, when the broadcast receiving equipment according to the present invention is intended to perform broadcast switching separately for video and audio, the received video condition sensing means may detect the conditions of the video of the received analog broadcast signals as the index of the received video condition and its received audio condition sensing means may detect the conditions of the audio of the received analog broadcast signals as the index of the received audio condition. If this configuration is implemented, higher quality video and audio outputs can be obtained from either digital or analog broadcasts, according to the conditions of the received analog broadcast signals.
The broadcast receiver according to the present invention may further include a received channel control means for controlling the digital broadcast receiver and the analog broadcast receiver to receive broadcasts of the same content on a pair of digital and analog channels as selected by the channel selection switch.
Alternatively, the broadcast receiver of the present invention may operate so that its analog broadcast receiver portion receives only the audio of analog broadcasts. In this mode, the receive condition sensing means senses the conditions of the audio of the received broadcast waves, the selection means selects either the audio of the digital broadcast or the audio of the analog broadcast, according to the received audio conditions sensed by the receive condition sensing means. If this operation mode is implemented, video output is obtained from digital broadcasts while and audio output is selectively obtained from whichever of either digital or analog broadcasts is of higher quality.
When the broadcast receiving equipment of the present invention is intended to make digital/analog broadcast selection for audio only, its receive condition sensing means may detect the error rate of audio packets during the demodulation of the received digital broadcast signals as the index of the received audio conditions. In this case, the equipment is preset so that its selection means will select the audio of the digital broadcast if the error rate of the audio packets detected by the received broadcast wave condition sensing means is less than a predetermined rate, or select the audio of the analog broadcast if this error rate is equal to or greater than the predetermined rate.
When the broadcast receiving equipment of the present invention is intended to make broadcast selection for audio only, its received condition sensing means may detect the received power level of the audio of the received digital broadcast signals as the index of the received audio condition. In this case, the equipment is preset so that its selection means selects the audio of the digital broadcast when the received power level of the audio of the received signals is greater than or equal to a predetermined level or selects the audio of the analog broadcast when this level is below the predetermined level.
A broadcast reception and output method according to the present invention comprises the steps of (a) receiving at least one digital broadcast channel and concurrently receiving an analog broadcast including a channel transmitting the same content as on at least one of the digital broadcast channels; and (b), selecting and outputting either a digital or an analog broadcast according to the conditions of the received digital or/and analog signal from a pair of digital and analog signals on which the same content is transmitted and which have been selected for reception.
According to the broadcast reception and output method of the present invention, when a pair of digital and analog of same content signals have been selected for reception, the received digital or analog signal having better wave condition can be output.
Step (b) of the broadcast reception and output method of the present invention can be implemented so that the error rate of packets during the demodulation of the received digital broadcast signals is detected as the index of the condition of the received waves. Then, the digital broadcast will be selected and output when the detected packet error rate is less than a predetermined rate and the analog broadcast will be selected and output when this error rate is greater than or equal to that predetermined rate. Determination as to whether the digital broadcast output is adequate can easily be made using the packet error rate.
Step (b) of the broadcast reception and output method of the present invention can alternatively be implemented so that the received power level of the received digital broadcast signals is detected as the index of the received broadcast wave condition. Then, the digital broadcast will be selected and output if the detected received power level is greater than or equal to a predetermined level or the analog broadcast will be selected and output if this level is lower than the predetermined level. Because the received power level is closely related to the received wave conditions, the better of either the digital or analog broadcast output can be used, according to the received power level.
Step (b) of the broadcast reception and output method of the present invention can further be implemented so that either the video of the digital broadcast or the video of the analog broadcast is selected and output, according to the received wave conditions of the video of the received broadcast waves, and either the audio of the digital broadcast or the audio of the analog broadcast is selected and output according to the received wave conditions of the audio of the received broadcast waves. In this way, more adequate audio and video can separately be output from digital or analog broadcasts.
When the broadcast reception and output method of the present invention will be applied to perform broadcast switching separately for video and audio step (b) may comprise the following sub-steps (b1) and (b2). In sub-step (b1), the error rate of video packets during the demodulation of the received digital broadcast signals is detected as the index of the received video condition. Then, the video of the digital broadcast will be selected and output when the detected error rate of the video packets is less than a predetermined rate or the video of the analog broadcast will be selected and output when this error rate is greater than or equal to the predetermined rate. In sub-step (b2), the error rate of audio packets during the demodulation of the received digital broadcast signals is detected as the index of the received audio conditions. Then, the audio of the digital broadcast will be selected and output when the detected error rate of the audio packets is less than a predetermined rate or the audio of the analog broadcast will be selected and output when this error rate is equal to or greater than the predetermined rate.
When the broadcast reception and output method of the present invention is applied to perform broadcast switching separately for video and audio, step (b) may alternatively comprise the following sub-steps (b1) and (b2). In sub-step (b1), the received power level of the video of the received digital broadcast signals is detected as the index of the received video condition. Then, the video of the digital broadcast will be selected and output when the detected received power level of the video of the received signals is greater than or equal to a predetermined level or the video of the analog broadcast will be selected and output when this level is below the predetermined level. In substep (b2), the received power level of the audio of the received digital broadcast signals is detected as the index of the received audio condition. Then, the audio of the digital broadcast will be selected and output when the detected received power level of the audio of the received signals is greater than or equal to a predetermined level or the audio of the analog broadcast will be selected and output when this level is below the predetermined level.